The internal combustion engine controllers for automobiles, motorcycles, farm vehicles, industrial machines, or ships which use gasoline or light oil as fuel are equipped with an injector (fuel injector) that injects fuel directly into cylinders to improve fuel consumption and engine output. Such a direct fuel injector uses high-pressure fuel and therefore requires a large amount of energy for valve opening operation. The direct fuel injector also requires having a short time for the energy to be supplied and interrupted in order to respond to an improvement in control performance (response) and to a high-speed rotation (high-speed control). That is, it is necessary to interrupt a current flowing in an electromagnetic load in a short time. Japanese Patent No. 3871168 discloses a conventional internal combustion engine controller that controls fuel injection.
In order to interrupt the current in the electromagnetic load in a short time and rapidly remove (consume) the large amount of energy from the electromagnetic load, a system has been proposed, for example, which transforms the energy into a heat energy using the Zener diode effect in a drive circuit. JP-A-2001-234793 discloses another system which regenerates the energy stored in the electromagnetic load into a booster circuit. The latter system may regenerate the energy using a regeneration element such as a regeneration diode. This system is widely utilized in direct-injection engines using gasoline as fuel because the system can relatively reduce heat generation in the drive circuit where a large current flows.
If some fault, such as battery short (short circuit to battery), ground short (short circuit to ground), short circuit to high-side driver, or open state, occurs in the electromagnetic load during driving or interrupting of the electromagnetic load, it is necessary to detect and diagnose the fault immediately. However, in a case of short drive cycle (that is, when the rotating speed of the internal combustion engine increases), the conventional internal combustion engine controllers cannot set a fault-detection timing control properly, and a diagnosis circuit may misdiagnose that short-circuit to a battery has occurred, for example, although the drive circuit and the electromagnetic load are normal. Moreover, an improvement in controllability may fail because it takes long time to return the potential of a diagnosis position to an initial state. In addition, the diagnosis circuit may misdiagnose due to unexpected disturbance such as noises.
Besides, if the regeneration element breaks down by overload energy, the energy cannot be regenerated, resulting in a possible serious accident, such as heat generation or ignition of the device.
An object of the present invention is to provide an internal combustion engine controller that drives an electromagnetic load such as an injector (fuel injector), improving a fault diagnosis precision of the electromagnetic load and stabilizing a high-speed control even when the rotating speed of an internal combustion engine becomes higher, that is, when the drive cycle of the electromagnetic load becomes shorter.
Another object of the present invention is to provide an internal combustion engine controller that is not influenced by noises.
Still another object of the present invention is to provide an internal combustion engine controller having a booster circuit of a battery voltage, with high reliability in fault diagnosis for a circuit that regenerates counter electromotive energy into the booster circuit as the counter electromotive energy is generated in driving of the electromagnetic load.